The situation in Spring 1942 was more favorable than anticipated. America had now entered the War after the bombing of Pearl Harbour on 7th December 1941. The failure of the German campaign in Russia in 1941 would mean that Germany would have to continue and complete the offensive in the East before committing to the invasion of Britain (indeed the German High Command had discussed the invasion of Britain in July 1941 and postponed the operation to Spring 1942 on the assumption the campaign against Russia would be completed – the operation was never seriously considered again).
The Anglo-American policy was to defeat “Germany First” and both America and Russia were pushing for offensive action on the Continent (Operation ROUNDUP which was later to become OVERLORD and Operation SLEDGEHAMMER which was later abandoned in favor of landings in North Africa, Operation TOURCH). Although Britain was in no position in 1942 to contemplate such operations, in June the Chiefs of Staff approved a memo by the C.I.C Home Forces suggesting that any invasion of Britain could not be contemplated until Germany had defeated Russia. Any successful invasion would require the German Air Force to defeat Britain’s Fighter defences. It would take at least three months to transfer all 1st line bombers and fighters from Russia and the Middle East fronts to the West. As collapse in Russia before August was very unlikely, there was no need to prepare detailed plans to meet an invasion in 1943. However large scale sea and airborne raids still had to be contemplated.
The following were considered as possible:
A large scale sea and airborne raid (one to three armoured divisions and four to five infantry divisions) could be mounted without weakening the Russian Front. However such an undertaking would require the Germans weakening their Air Force in the Russian and Middle East fronts and was thus considered unlikely. The concentration of shipping for such a raid and the withdrawal of the German Air Force would give several weeks notice.
A small scale sea and airborne raid (between company and battalion strength) could be mounted without prior warning. Such a raid would be targeted against a small but vital objective on the coast.
A large scale airborne raid of 100,000 parachutists and airborne troops against industry and fighter aerodromes. It was anticipated that it would take between 7-10 days to land such a force. The landings would have to take place during the night if Germany did not obtain air superiority. To obtain air superiority (Germany had already failed once in trying to achieve this) would again involve Germany weakening her Air Force in other fronts so was considered unlikely.
The C.I.C produced an appreciation of the Home Defence Plan for 1943 on Sept 28th. The growing number of American forces in Britain, and their inevitable appearance in the Western theatre of war, and the inconclusiveness of the battle of the Atlantic may tempt Germany to launch a last attempt to win the war by the invasion of Britain in 1943 if Russia could be defeated or the situation on the Eastern front stabilized at least. He considered that such an attack would be launched against South Eastern Command with the target being London and could involve 10 armoured divisions (approx 2,000 tanks) and 21 infantry divisions.
The Chiefs of Staff did not agree with this and considered any attempt at invasion in 1943 to be negligible. The principal reasons for this were the combined American and British air force which would be able to drop 47,000 tons of bombs on the invasion ports in seven days. The naval situation had also by now improved markedly – a large force of light naval units could meet the invasion flotilla and be fully reinforced with ships from the Western Approaches in four days.
The Chiefs of Staff also considered that it was “inconceivable that the Germans would be able to obtain the requisite degree of air superiority for an invasion to be practicable before 1944, if ever”. They also pointed out that by 1943, five American divisions would be present in Britain and that there would be no problems in reorganizing and deploying the forces in Britain to meet such a threat. Such was the confidence now that from Easter Sunday 1943, church bells could again be rung (they had been silent since June 1940 except to warn against parachutist or airborne attack).
Defence Plans for the United Kingdom, TNA
Appreciation of German Airborne Invasion, TNA